Quantum cascade lasers with voltage defect of less than one longitudinal optical phonon energy

Efficient use of applied voltage in quantum cascade (QC) lasers is a critical factor in achieving high wall-plug efficiency and low compliance voltage. We demonstrate a QC laser emitting at 4.2 μm featuring a low voltage defect and short injector with only four quantum wells. Devices with a voltage defect of 20 meV, well below the energy of the longitudinal optical phonons, and a voltage efficiency of 91%, a record value for QC lasers, are reported for pulsed operation at 180 K. Voltage efficiencies of greater than 80% are exhibited at room temperature. Overall performance showed wall-plug efficiencies ranging from 21% at cryogenic temperatures to 5.3% at room temperature.